Retinitis pigmentosa (RP) is a genetic eye condition that results in damage to the retina. It has no cure; over time, a person with RP loses much or all of their vision.

But scientists have gotten one step closer to finding a better treatment. Researchers at the RIKEN Institute in Japan have now succeeded in growing retinal tissue and transplanting that tissue into the retinas of rhesus monkeys with RP. Three weeks after the treatment, visual tests on two of the monkeys found their vision had improved.

In the study, published this week in the journal PNAS, researchers grew retinal tissue from stem cells and then transplanted the tissue into the retinal area of rats with advanced RP. The tissue grew and in some cases adhered to the cells already in the retina and formed connections—a key factor in the success of this approach.

Then, the researchers tried a similar approach on rhesus and macaque monkeys with end-stage RP. Similarly, the retinal cells grew and formed connections and synapses, allowing the new retinal tissue to connect and "talk to" the retinal cells already there. In order for a tissue graft like this to be successful, the cells need to not only grow and differentiate from stem cells but also connect to the cells already there to become one unit.

The researchers say that future studies will allow them to better understand how often the implanted retinal tissue is likely to form connections with the retinal cells already there. And while therapy like this for humans is still far out, they say that the monkey models will help them optimize for conditions that they would expect to see in humans.